PTL 1 discloses a recovery method to recover a hierarchical storage system running at high speed by reducing the time required for recovering the hierarchical storage system. In this method, a hierarchical storage system running on an operating system includes: a first storage apparatus having a file system which has inodes containing attribute information of files and uniquely identifies the files using inode numbers; and a second storage apparatus which stores data including backup data of the file system. When the file system is restored in the first storage apparatus by using the backup data in the second storage apparatus, the inode number of a restoration target file is designated using an inode number contained in the backup data so as to allocate the designated inode number to the restoration target file in the file system.
PTL 2 discloses a hierarchical storage management (HSM) control method for controlling an HSM including a first storage and a second storage to efficiently manage backup generations of name spaces in the HSM. This HSM control method includes: every time backup is performed in the HSM, creating the generation information containing the generation number of the backup; and managing a name space information history which includes name space information that is information on the name space per file in the HSM, and includes a valid generation number range indicating a range of generation numbers with valid name space information by using the generation numbers created in the generation information creating step.